docs(agent-skill): existing installs that stored off are switched on once

The changeset, CLAUDE.md, the invariants, the agent control plan, both READMEs
and the wiki's Codeman Skill and Settings Reference pages said an install whose
App Settings were saved on an earlier version stays off until switched on. They
now say the first 1.50.0 start switches a stored off on once, and that turning
it off afterwards sticks. The changeset marks it "Behaviour change:", says the
migration cannot tell a chosen off from the old default, and tells users to
reload a tab left open from before the upgrade before saving App Settings in
it. CLAUDE.md lists the marker file among the data dir's state files, and the
invariants record why it stores true, why the marker is its own file, and
where it runs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.changeset/agent-skill-default-on.md

@@ -2,4 +2,4 @@
 'aicodeman': minor
 ---
 
-**The Codeman agent skill is on by default.** New sessions get the skill in their folder, where their CLI looks for skills (`.claude/skills/codeman/` for Claude Code, `.agents/skills/codeman/` for Codex, Gemini CLI, OpenCode, Antigravity, Grok, DeepSeek and OMP; still none for Pi, GitHub Copilot or a plain shell), so an agent can start and drive workers without an install step. The copy now ignores itself in git (a `.gitignore` of `*` inside the copy, written once and never overwritten), so it never shows up as a new file in your repository, and `codeman skill uninstall` removes it with the copy. A `settings.json` without the `agentSkillEnabled` key now means on; an explicit `false` stays off, which includes every install whose App Settings were saved on an earlier version, since that save wrote the old default. Turn it off under App Settings, Agents & CLIs, All agent CLIs, **Codeman Agent Skill**. Turning it off still removes no copy already written: `codeman skill uninstall --case <name>` does that per case.
+**The Codeman agent skill is on by default.** New sessions get the skill in their folder, where their CLI looks for skills (`.claude/skills/codeman/` for Claude Code, `.agents/skills/codeman/` for Codex, Gemini CLI, OpenCode, Antigravity, Grok, DeepSeek and OMP; still none for Pi, GitHub Copilot or a plain shell), so an agent can start and drive workers without an install step. The copy now ignores itself in git (a `.gitignore` of `*` inside the copy, written once and never overwritten), so it never shows up as a new file in your repository, and `codeman skill uninstall` removes it with the copy. A `settings.json` without the `agentSkillEnabled` key now means on. **Behaviour change:** every Save of App Settings on 1.49.0 or earlier wrote the old default (`false`) whether or not you touched this switch, so on its first start 1.50.0 switches a stored off on, once per data directory (it cannot tell an off you chose from the old default; the startup log says when it did). Turn it off under App Settings, Agents & CLIs, All agent CLIs, **Codeman Agent Skill**: an off set after that first start stays off. A browser tab left open from before the upgrade still holds the old value until you reload it, so reload before saving App Settings there. Turning it off still removes no copy already written: `codeman skill uninstall --case <name>` does that per case.